This package appears to ship a .sass-cache/ directory, the result of running a the "Sass" utility that compiles CSS from SASS or SCSS files.
These are not useful in the binary package or to end-users. In addition, as they contain random/non-determinstic contents or filenames they can affect the reproducibility of the package.
Please ensure they are removed prior to final package build. For example, with:
override_dh_install: dh_install -X.sass-cache